Dineutus (Rhombodineutus) heurni Zimmerman, 1924

Polhemus, Dan A., 2011, New distributional records for Gyrinidae (Insecta: Coleoptera) on New Guinea and nearby islands, with a checklist of the New Guinea species, Zootaxa 2900, pp. 51-68 : 55-56

Dineutus (Rhombodineutus) heurni Zimmerman, 1924

Fig. 3

Dineutes Heurni Zimmerman, 1924: 2 .

Dineutes obscurus Zimmerman, 1924: 1 . Syn. by Ochs, 1955: 139. Dineutus (Rhombodineutus) heurni: Ochs, 1926: 140 .

Material examined. INDONESIA, Papua Prov. [= former Irian Jaya Prov.]: 5 males, 3 females, Wapoga River basin, upper Ziwa River at PTFI Wapoga Alpha drilling camp, 1050 m. [3500 ft.], 3°08'41"S, 136°34'25"E, water temp. 19° C., 19 April 1998, 08:00–12:00 hrs., CL 7101, D. A. Polhemus ( USNM); 2 males, 2 females, Wapoga River basin, rocky rainforest tributary to upper Ziwa River at PTFI Wapoga Alpha drilling camp, 1050 m. [3500 ft.], 3°08'41"S, 136°34'25"E, water temp. 20° C., 18 April 1998, 10:00–17:00 hrs., CL 7100, D. A. Polhemus ( USNM); 1 female, Wapoga River basin, Tirawiwa River and overflow channel at abandoned Wapoga Timber Company camp, 2.0 km. S. of PTFI Siewa exploration camp, 60 m. [200 ft.], 3°03'20"S, 136°23'31"E, water temp. 27° C., 10 April 1998, 08:30–11:30 hrs., CL 7094, D. A. Polhemus ( USNM); 1 male, 2 females, Wapoga River basin, rocky tributary to Logari River, approx. 0.5 km. W. of PTFI Landing Site 21, 295 m. [970 ft.], water temp. 25° C., 6 April 1998, 12:30–14:30 hrs. 3°00'27"S, 136°33'14"E, CL 7091, D. A. Polhemus ( USNM).

Discussion. This species was described from material collected by the Archbold Expeditions in the mountains bordering the Idenberg River of western central New Guinea. New collections have now extended the range of D. heurni well westward into the adjacent Wapoga River Basin ( Fig. 3 ).

This species was found across a relatively wide range of elevations and ecological settings within the Wapoga River catchment. The Tirawiwa River site was a broad, open, unshaded river flowing through a braided gravel bed after emerging from the northern foothills of the New Guinea central mountains and onto the coastal lowlands. At this locality the gyrinids were taken from eddies along the river margins just downstream of steeply cut banks formed on the outside edges of channel bends. By contrast, the Logari River site where this species was taken was a swift, deep river running in a bed of boulders, rocks and cobbles occupying a narrow valley within the foothills of the central ranges. The river channel was unshaded in the center, whereas the margins were heavily shaded by primary rain forest; the gyrinids were taken from along these shaded margins below a set of rocky rapids.

At the Tirawiwa River site noted above, this species was syntopic with both Dineutus (Rhombodineutus) tetracanthus tetracanthus and Dineutus (Rhombodineutus) sinuaticollis , while at the Logari River site it was syntopic with only the latter species. Moving still further uphill in the Wapoga Basin, D. heurni was syntopic with the much larger Dineutus (Merodineutus) archboldianus at the Ziwa River, where a very swift, clear, and powerful mountain river came crashing down through a largely unshaded bed of boulders and bedrock. At this latter locality the gyrinids were found on a sheltered pool formed where a small, clear tributary joined the much faster main stream. Across the Wapoga River Basin as a whole, D. (R.) heurni therefore appears to be a relatively constant member of local gyrinid assemblages that otherwise demonstrate marked species turnover with increasing altitude.

Based on known collections, D. heurni occupies the Mamberamo Foreland area of freshwater endemism (Area 17) as defined by Polhemus & Allen (2007), being found in the foothill and premontane zones along the southern margins of both the Mamberamo and Wapoga river basins.

This species, in combination with Dineutus (Rhombodineutus) tetracanthus tetracanthus and Dineutus (Rhombodineutus) sinuaticollis , was grouped under the composite listing of “ Rhombodinetus sp. undet.” from Station 50 in Polhemus (2000). It is also the species listed as “ Rhombodineutus sp. undet.” from Station 58 in that same publication.

Figures

FIGURE 3. Distribution of certain Dineutus (Rhombodineutus) species on New Guinea. Symbols with grey centers represent previous records; symbols with black centers represent new records presented in this paper.